Global warming could lead to more people in Britain suffering the misery of asthma, research suggests.

A study of almost 670,000 children has found a clear link between indoor humidity and asthma rates in Western Europe.

Every 10pc increase in indoor humidity was associated with a 2.7pc increase in the prevalence of asthma symptoms.

House dust mites, which trigger asthma attacks, thrive in moist air and humidity encourages mould, which can irritate the airways.

The study also found that places where average outdoor humidity dropped below 50pc for at least one month a year had lower rates of asthma.

Experts believe summers in the city will get stickier because of the "urban heat island" effect caused by asphalt and concrete trapping heat at night.

The impact of climate change was acknowledged by the authors of the asthma study, led by Dr Stephen Weiland, of the University of Ulm in Germany.

Writing in the journal Occupational and Environmental Medicine, they said the evidence showed climate could affect rates of asthma and eczema in children.

They said: "This may also have implications for the assessment of potential health effects due to climate change." The scientists found that temperature, altitude, humidity and latitude all influenced asthma and eczema.

Information was collected between 1992 and 1996 from children aged six to seven, and 12 to 13, from more than 50 countries.

The research was part of a worldwide investigation, the International Study of Asthma and Allergies in Childhood. It found a strong link between humidity and asthma.